In recent years, magnetic disk drives having dual-stage actuators (DSAs) have been developed. A dual-stage actuator comprises not only a voice coil motor (VCM) actuator but also at least one microactuator. Here, given a magnetic disk drive having a plurality of heads, a microactuator is provided in each of a plurality of suspensions that support the plurality of heads. The microactuator has a narrower range of motion than the VCM actuator but exhibits a high following capability at high frequency.
On the other hand, actuators that are currently in use comprise no microactuator. Such an actuator is referred to as a single-stage actuator (SSA).
As is well known, a plurality of heads are simultaneously moved in one direction by the VCM actuator. However, the relative positions of the plurality of heads in a radial direction of a disk are not necessarily the same because of variation in the mounting of the plurality of suspensions that support the plurality of heads. In the description below, the position of the head refers to the position in the radial direction of the disk.
For example, if the position of a first head is defined as a reference position, the position of a second head (relative position) is generally displaced from the reference position. Thus, if the switching (what is called head switching) from the first head to the second head takes place, the displacement affects a seek operation involving the head switching. The displacement is referred to as an inter-head offset.
Thus, the conventional art measures the offset between the first head and the second head. To switch from the first head to the second head, the conventional art estimates the position of the second head based on the result of the measurement and the position of the first head.
However, a magnetic disk drive having a dual-stage actuator may apply any voltage to each of a plurality of microactuators associated with a plurality of heads. The plurality of microactuators are displaced depending on the applied voltages, and the plurality of heads are also displaced according to the displacement of the microactuators. Furthermore, the plurality of microactuators individually vary in gain. Thus, even if the same voltage is applied to the plurality of microactuators, the displacements vary among the plurality of heads. Thus, there has been a demand for a magnetic disk drive having a dual-stage actuator which allows the head position to be corrected during head switching in view of the displacements of the heads resulting from the operation of the microactuators.